This invention relates to a rehydratable product or membrane especially suitable for use in an iontophoretic bioelectrode system, and to a method of preparing the rehydratable membrane.
Iontophoretic bioelectrodes, used in place of hypodermic needles to inject medications into a person's skin or tissue, typically include a pouch or similar enclosure formed with a wettable barrier or a microporous membrane on one side thereof. See, for example, U.S. Pat. Nos. 4,250,878, 4,419,092 and 4,477,971. A medication solution containing ions to be delivered into the person's skin or tissue is injected into the pouch by means of a hypodermic needle, syringe, etc. When the wettable barrier or membrane is placed against a person's skin and an electric current is supplied to the solution, the ions are caused to migrate from the solution through the wettable barrier or membrane, and into the skin.
A second bioelectrode is used in conjunction with the above-described iontophoretic bioelectrode, but does not include a solution of ions. Rather, the second bioelectrode need only include an element for making contact with the person's skin or tissue (generally in close proximity to the iontophoretic bioelectrode), such as a wettable barrier or membrane for allowing migration of current (of opposite polarity to that of the current supplied to the iontophoretic bioelectrode) between the person's skin or tissue through the contact element to a second current source.
For the iontophoretic bioelectrode described earlier, barriers or membranes are required to retain the solution in the pouch while allowing ions to migrate therethrough. However, such barriers or membranes also inhibit wetting of the skin and thus inhibit the migration of ions to a certain extent, at least as compared to a situation where the solution were in direct contact with the skin. Also, because of the use of a pouch or similar enclosure to contain the medication solution, a mechanism or structure on the enclosure is necessary for allowing the injection thereinto of the solution. Such structure has typically included some type of orifice containing a plug into which a hypodermic needle or syringe tube may be inserted to allow delivery of the solution through the orifice into the interior of the enclosure, while preventing the outflow of the solution after it has been injected into the enclosure. The requirement of such solution receiving mechanism or enclosure, of course, increases the cost of the bioelectrode and gives rise to potential leakage locations.
In copending patent application, Ser. No. 383,939, a hydratable bioelectrode is disclosed in which the need for special solution receiving structure or mechanisms is obviated. This bioelectrode includes a layer of material for absorbing and holding aqueous solutions when placed in contact therewith, a conductive sheet disposed in close proximity to the layer of material for receiving an electrical charge to thereby cause ions in the fluid to move to and from the layer of material toward or away from the conductive sheet, and a support base on which the layer of material and conductive sheet are mounted. The layer of material may comprise a polymer, a matrix of fibers impregnated or interwoven with a hydratable polymer, or similar ion solution absorbing material. This bioelectrode structure provides a simple, inexpensive and easy to use iontophoretic delivery mechanism.